In an electrophotographic photosensitive member used in an electrophotographic apparatus, an undercoat layer containing metal oxide particles is disposed between a support and a photosensitive layer. The metal oxide particles are surface-treated with a silane coupling agent for preventing image defects of black spots due to charge injection from the support to the photosensitive layer.
Recently, the requirement for a reduction in variation of light potential of an electrophotographic photosensitive member in repeating use has been increased than ever before in association with speed-up (acceleration of process speed) of electrophotographic apparatuses. In particular, in an undercoat layer containing surface-treated metal oxide particles, the resistance of the undercoat layer is increased, and the potential (such as light potential) is apt to significantly vary in repeating use.
As technologies of preventing the variation in light potential of an electrophotographic photosensitive member, PTL 1 describes an undercoat layer containing zinc oxide particles provided with an acceptor compound (organic compound); PTL 2 describes an undercoat layer containing metal oxide particles having surfaces provided with a dye (organic compound) that absorbs light in a wavelength range of 450 to 950 nm; and PTL 3 discloses a plurality of undercoat layers containing a silane coupling agent such that the concentration of the silane coupling agent in the undercoat layer on the support side is higher than others.
Unfortunately, investigation by the present inventors resulted in that the technologies disclosed in PTLs 1 to 3 have the following problems: Though the variation in light potential can be sufficiently prevented in repeating use under an ordinary temperature and ordinary humidity (23° C./50% RH) environment, the variation in light voltage cannot be sufficiently prevented in repeating use under a high temperature and high humidity (30° C./85% RH) environment in some cases.